1. Field of the Invention
The present invention relates to a heating apparatus for a vehicle, in which a heat-generating unit using a shearing force, for increasing a temperature of cooling water for cooling a water-cooled engine, is switched based on a load applied to a hydraulic pump of a power steering device.
2. Description of Related Art
Conventionally, as a heating apparatus for a vehicle, a hot water type heating apparatus for heating a passenger compartment has been generally known. In the hot water type heating apparatus, cooling water for cooling a water-cooled engine is supplied to a heater core disposed in a duct, and air heated while passing through the heater core is blown into the passenger compartment by a blower to heat the passenger compartment of the vehicle.
In recent years, it is desired to improve an efficiency of the engine installed in an engine compartment. When the efficiency of the engine is improved, a load of the engine is decreased so that cooling water for cooling the engine cannot be sufficiently heated. Further, in a case of a vehicle having a diesel engine or a lean burn engine, heat generated in the engine is too small to heat the cooling water with engine sufficiently. In this case, because a temperature of cooling water to be supplied to a heater core cannot be maintained at a predetermined temperature (e.g., 80.degree. C.), there occurs a problem in that a heating capacity for the passenger compartment is insufficient.
To overcome such a problem, as disclosed in U.S. Pat. No. 4,993,377 and JP-A-3-57877, the following heating apparatus for a vehicle is conventionally proposed. In the heating apparatus for a vehicle, a heat-generating unit using a shearing force, for heating cooling water to be supplied to a heater core from an engine, is disposed in a cooling water circuit, and the heat-generating unit is operated when the cooling water temperature is lower than a set cooling water temperature to improve the heating capacity for the passenger compartment.
The heat-generating unit transmits a driving force of the engine to a shaft through a belt transmitting mechanism and the electromagnetic clutch. A heat-generating chamber is formed in a housing of the heat-generating unit, and a cooling water passage is formed at an outer periphery of the heat-generating chamber. A rotor which rotates integrally with the shaft is disposed in the heat-generating chamber, and a shearing force generated by a rotation of the rotor is applied to viscous fluid such as silicon oil having a high viscosity, sealed in the heat-generating chamber to generate heat. The cooling water circulating in the cooling water passage is heated by the generated heat.
Further, in recent years, a power steering device is generally installed in a vehicle to simplify a driver's steering operation. In the power steering device, a driving force of an engine is transmitted to a hydraulic pump through a belt to generate a hydraulics as a driving source of the device. However, when a driver performs a steering operation when the vehicle is stopped, a load applied to the hydraulic pump of the power steering device becomes larger, and therefore a large driving load is applied to the engine. At this time, if the heat-generating unit is operated to increasing the heating capacity for a passenger compartment, a large driving load is further applied to the engine.
As a result, the engine may be stopped and a belt of the hydraulic pump slides, and therefore the hydraulic pump is not normally operated and a noise is caused. When a belt is hung on both of a rotor of the hydraulic pump of the power steering device and a rotor of the heat-generating unit, the above-described problems are readily caused. However, even if both belts are respectively hung on the rotor of the hydraulic pump and the rotor of the heat-generating unit, the above-described problems may be caused.